Immediate and high speed access to the vast amount of digital information available today is in critical demand for home entertainment, business communications and wireless communication devices.
One example of this demand, and the resources being applied to fulfill it, is the “triple play” effort being put forth by cable and telephone companies to supply high-speed internet access, television programming and telephone service over a single broadband connection.
For the telephone companies, the triple play is delivered to a resident or a business using a combination of optical fiber and Asynchronous Digital Subscriber Line (ADSL) technology. This configuration uses optical fiber to reach areas at long distances from the telephone central office, and uses ADSL or VDSL (Very-High-Data-Rate Digital Subscriber Line) over an existing TTP as the last mile to the home or business. This two step approach is necessary as Digital Subscriber Line (DSL) technology suffers from significant degradation in bandwidth over long distances.
It has been estimated that the bandwidth required to provide advanced triple-play services will require a downstream (head end or central office to residence or business) data rate of between 37 and 57 Mbits/sec. This is based on an average of 3 High Definition TV (HDTV) sets per household requiring 9-12 Mbits/sec each, high speed internet at 10-20 Mbits/sec, and IP voice at 0.25 Mbits/sec.
There are a number of basic DSL services for possible use with a triple play service; including ADSL, ADSL2+ and VDSL. ADSL can provide a downstream bandwidth of approximately 2 Mbits/sec at a distance of 18,000 feet, and 6 Mbits/sec at a distance of 6000 feet. ADSL 2+ can provide an approximate bandwidth of 25 Mbits/sec at 3000 feet using a second twisted pair. VDSL can provide an approximate bandwidth of 25 Mbits/sec at 3000 feet and the possibility of 57 Mbits/sec at 1000 feet using a second twisted pair. Therefore in order for a telephone company to provide a full service triple play configuration with existing DSL technology, it is necessary to install fiber optic networks which are accessible within approximately 1000 feet of every home or business.
Cable television operators face a similar problem as the majority of their current installations are Coaxial cable which cannot support the required bandwidth over long distances. Therefore they must also install fiber optic networks and use available coaxial cable, rather than a TTP for the last transmission mile. For cable companies the Hybrid Fiber Coaxiel (HFC) architecture is used for television programming and high-speed Internet access, while Voice over IP (VOIP) is used to deliver telephone service.
It is estimated that U.S. phone companies alone will have to spend more than $26 Billion to install the fiber optic networks needed for triple play service.
For wireless communications, advances in Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM) standards are also providing another medium to deliver video, Internet access and voice telephone service. Thus the triple play is becoming the “quadruple play” which means greater demand for available bandwidth. This demand is shown by the recent 700 MHz auction in the U.S. which yielded $19 Billion in bids while telephone companies in the U.S. have bid $71 Billion for spectrum since 1995.
The goal of the present invention, to increase the information carrying capacity for any type of communications highway, requires an understanding of the basic theory underlying channel capacity as developed by Claude Shannon and Ralph Hartley. The Shannon-Hartley Theorem is an application of the noisy channel coding Theorem to the archetypal case of a continuous-time analog communications channel subject to Gaussian noise. The theorem establishes channel capacity, a bound on the maximum amount of error-free digital data (pulse based information) that can be transmitted over a communication link, with a specified bandwidth and in the presence of the noise interference. The theorem is based on the assumption that the signal power is bounded and the Gaussian noise process is characterized by a known power or power spectral density. To achieve this goal, conventional methods attempt to increase the number of bits per single modulating frequency using efficient technology enhancements. The improvement is limited since noise on the channel remains the same. The present invention sends multiple frequencies, each on its own virtual channel, with minimal increase in total physical channel bandwidth and ensures that each modulated frequency achieves maximum capacity within the constraints of the Shannon limit. The combined information throughput is the sum of capacities for all virtual channels. In essence the proposed invention provides a methodology for combining many virtual channels within the same constrained channel bandwidth that no other known systems can achieve.
Considering all possible multi-level and multi-phase encoding techniques, the Shannon-Hartley theorem states that the channel capacity C, meaning the theoretical upper bound on the rate of clean (error free) data that can be sent with a given average signal power S through an analog communication channel subject to additive white Gaussian noise of power N is given by;C=B log2(1+S/N)                where:                    C is the channel capacity in bits per second,            B is the bandwidth of the channel in hertz,            S is the total signal power over the bandwidth, measured in watts,            N is the total noise power over the bandwidth, measured in watts, and S/N is the signal-to-noise ratio (SNR) of the communication signal to the Gaussian noise interference, expressed as a straight power ratio.                        
The Shannon-Hartley Theorem establishes what the channel capacity is for a finite-bandwidth continuous-time channel subject to Gaussian noise. It also makes it clear that bandwidth limitations alone do not impose a cap on maximum information rate. That is because it is possible for a digital pulse signal to take on an indefinitely large number of different voltage levels on each symbol pulse, with each slightly different level being assigned a different meaning or bit sequence. However, when noise and bandwidth limitations are combined, the Shannon-Hartley Theorem taught that there was a finite limit to the amount of information that could be transferred by a signal of a bounded power even when various multi-level encoding techniques are used.
The finite limit on channel capacity postulated by the Shannon-Hartley Theorem is based in part on the fact that in the channel considered by this theorem, noise and signal are combined by addition. That is, the receiver receives a signal that is equal to the sum of the signal encoding the desired information and a continuous random variable that represents the noise. This addition creates uncertainty as to the value of the original encoded signal.
The Shannon-Hartley Theorem has been applied to all conventional communications systems and provides maximum data rate supported given the bandwidth of the channel and the Signal to Noise Ratio. In conventional systems, the modulated frequencies are not overlapped within nearly the same bandwidth, rather, each modulated frequency has a distinct bandwidth. Thus, to increase the data rate in conventional communications systems, bandwidth has to be increased. The Shannon-Hartley theorem is also applied to the proposed inventive technology described herein. However, the inventive technology described herein allows increased capacity due to the cumulative sum of multiple virtual channels with each having a modulated frequency (carrier) close to each other and still maintain nearly the same total bandwidth on the physical channel. In addition, as all these modulated frequencies (virtual channels) are transmitted onto the physical channel simultaneously their bandwidths significantly overlap. To recover the increased data capacity, the inventive technology suppresses the inter-carrier interference significantly by a combination of a Transmit Super Resonant Filter (TXSRF) at the transmitter, a Receiver Super Resonant Filter (RXSRF) and a Matched Filter, all of which are described below.
One type of noise is one or more data-carrying interfering carriers which occupy substantially the same bandwidth as the desired carrier signal. The inventive system utilizes spectrally overlapping data-carriers in a unique combination (using the Transmit and Receive SRF circuits) to increase the overall throughput of a transmission system, while neither increasing the overall signal bandwidth (as in spread-spectrum systems), nor by decreasing the SNR (as in multi-user CDMA systems). Finally, the inventive system's implementation of overlapping carriers is superior to orthogonal systems (such as Orthogonal Frequency Division Multiplexing (OFDM). Unlike the instant invention, OFDM systems are limited in that the choice of frequencies for separating carriers is very precisely set by rules of orthogonality, resulting in a marginal increase in overall data throughput for a given bandwidth.
The inventive process described below causes the difference between the cumulative energy of the signal and the cumulative energy of noise to become greater. This results in a significantly increased channel capacity heretofore not thought achievable. Since the modulated frequencies of different channels overlap within a constrained bandwidth, inter-carrier interference is more dominant than other noise. The present invention reduces the impact of all of the noise to increase the overall capacity. This decoupling of the noise and signal bandwidth achievable with the present invention represents a completely novel application of the Shannon-Hartley Theorem.
A basic reason for the inventive improvement in channel capacity described herein is the present invention does not rely on a digital pulse signal to convey information. Rather, the present invention transmits information by communicating the amplitude of discrete sinusoidal signals that remain fixed in amplitude in the same period in which the change in status at the transmitter is occurring. There is no abrupt change in amplitude from one bit period to the next as there is when information is sent as a pulse. Each discrete interval has its own sine wave inputs that develop as sine waves with time. This means that there are no sources of wide band spectra in this communication system as there is when information transfer is based on digital pulses.
The present invention provides for a huge improvement in the signal-to-noise ratio by blocking the detrimental effect of all channel noise except for the noise resident within a narrow bandwidth carrying the transmitted information signal.